This invention relates to ophthalmic lenses, and more particularly to ophthalmic lenses having progressively varying focal power.
Progressive multifocal lenses are intended to provide a person, particularly one of advanced age whose ability to control his crystalline lenses has weakened, with an ophthalmic lens for compensating for this loss. The progressive multifocal lenses have three zones, namely, a far vision viewing zone, a near vision viewing zone and an intermediate vision viewing zone having progressively varying focal power. The zones are referred to as a far zone, a near zone and an intermediate zone.
Progressive multifocal lenses have an aspherical surface, and as a result, astigmatism and distortion of images are inevitably caused. In order to provide an improved lens it has been sought to distribute astigmatism uniformly throughout the entire surface of the lens in an effort to reduce image distortion and to reduce the shaking of the image when the wearer moves his face. Several issued U.S. patents suggest solutions, such as U.S. Pat. Nos. 3,687,528 and 3,910,691. Additionally, U.S. Pat. Nos. 4,055,379, 4,056,311 and 4,062,629 provide a clear viewing zone in the far zone and in the near zone for a large area and concentrate astigmatism in the peripheral portions of the clear viewing zone.
These proposals have not been entirely satisfactory and further improvements are necessary. Accordingly, it would be desirable to provide a progressive multifocal lens having reduced astigmatism and image distortion. Additionally, it is desirable to provide such benefits by reducing skew distortion in the far zone and in the near zone.